1. Field of the Invention
The present invention relates to a metal-containing indoaniline compound useful for optical recording which utilizes the laser technology and an optical recording medium employing the compound.
2. Discussion of Background
In recent years, the optical recording utilizing laser has been developed particularly for the storage of high density information recording and reproduction of the recorded information.
An optical disc may be mentioned as a typical example of such optical recording medium.
In general, the optical disc is designed for high density information recording which is effected by irradiation of a laser beam collimated to have a diameter of about 1 .mu.m onto a thin recording layer formed on a substrate of a disc shape. The information recording is effected by a thermal deformation of the recording layer, such as the decomposition, evaporation or dissolution, which takes place upon absorption of the laser beam energy at the irradiated portions of the recording layer. On the other hand, the reproduction of the recorded information is done by reading a difference in the reflectance between the portion thermally deformed by the laser beam and the portion where no such deformation has occurred.
Accordingly, the optical recording medium is required to have high absorptivity for a laser beam of a particular wavelength used for the recording since it is required to absorb the energy of the laser beam efficiently, and also to have a high reflectance to the laser beam of a particular wavelength for use in the reproduction so as to carry out the accurate reproduction of the recorded information.
Various constructions have been proposed for the optical recording medium of this type.
For example, Japanese Unexamined Patent Publication No. 97033/1980 discloses a medium having a single layer of a phthalocyanine dye formed on a substrate. However, the phthalocyanine dye is poor in the sensitivity and has a difficulty such that its decomposition temperature is high and its vapor deposition is difficult. Besides, its solibility in an organic solvent is extremely poor, and it is hardly possible to apply it by coating.
Japanese Unexamined Patent Publication No. 83344/1983 discloses a recording medium having a recording layer composed of a phenalene dye, and Japanese Unexamined Patent Publication No. 224793/1983 discloses a recording medium having a recording layer composed of a naphthoquinone dye. However, such a dye has a drawback that the reflectivity is low while it has an advantage that it can readily be vapor-deposited. If the reflectivity is low, the contrast in the reflectance between the non-recorded portion and the recorded portion irradiated with the laser beam tends to be low, and the reproduction of the recorded information tends to be difficult. Further, in general, an organic dye has a drawback that it is inferior in the storage stability.